The present invention relates to an apparatus of dedusting gases by electrostatic precipitation at temperatures above 400.degree. C.
A process for dedusting gases by electrostatic precipitation at temperatures above 400.degree. C. is known, in which the dust-laden hot gas is conducted through at least one passage defined by a tubular collecting electrode or by two plate-like collecting electrodes in which at least one discharge electrode is centrally disposed.
In the publication, "Heissgasentstaubung" by R. Pitt, Sonderlosungen der Lufteinhaltung, March 1989, L 4 to L 9, it has been pointed out that electrostatic precipitators have been satisfactory components of power plants, if the exhaust gases are at standard temperatures. It is also apparent from that publication that the degree of separation of dust from the gases under conditions which are otherwise equal increases as the temperature of the gases increases, because the viscosity and the volume flow rate of the gas increase with temperature. According to this publication it is not desirable to increase the collecting surface area to compensate for a rise in temperature, because a precipitator with this increased collecting surface area would have a larger size and thus would be more expensive and there would be a higher temperature drop. For this reason it is proposed in this publication to increase the electric field strength at higher operating temperatures, if this is possible without a flashover. The permissible field strength is favorably influenced by a higher gas pressure and the resulting higher gas density. At higher operating temperatures dust must be retained on the collection electrode and compacted to a sufficiently thick layer for the cleaning of the collecting electrode.
It has been found that in operation of known electrostatic precipitators, such as have been described in Ullmanns' Encyklopadie der technischen Chemie, 4th Edition, Volume 2, pp. 240 to 247, considerable difficulties arise in the case of normal gas pressures, if the operating temperature exceeds 400.degree. C. Approximately at that temperature limit the current-voltage characteristic exhibits an unfavorable change unless the gas pressure is increased to 3 to 5 bars. The separation efficiency also is reduced, because the differential thermal expansions of different materials result in electrode spacing changes and, as a result, in disturbances of the electric field. Besides the materials used result in strength problems.